1. Field of the Invention
The present invention relates to phenolic resin composition usable as molding materials, laminating materials, paints and lacquers, adhesives, binders for shell molds, grindstones, brake linings, etc., casting materials, foaming agents, etc.
Further, the present invention relates to molding phenolic resin compositions.
2. Description of the Prior Art
Polymeric substances having a phenolic OH group, employable in the present invention, include phenolic resins, alkenylphenolic polymers, copolymers of alkenylphenols with other polymerizable monomers, polymeric substances derived from phenolic compounds and paraxylylene dihalides or paraxylylene dialkyl ethers, etc. Polymers having a phenolic OH group other than phenolic resins will be hereinafter abbreviated to phenolic polymers.
As is well known, phenolic resins include general-purpose novolak type phenolic resins, novolak type phenolic resins having a high content of ortho bond and resol type phenolic resins. As for these resins, after heat treatment thereof (if necessary, a formaldehyde-generating compound such as hexamethylenetetramine being added thereto prior to the treatment), the resulting cured substances have been employed for various uses. Namely the resins have been widely used as molding materials, laminating materials, paints and lacquers, adhesives, various binders for shell molds, grindstones, brake linings, etc., casting materials for ornamental goods, tools, tablewares, etc., foaming materials, etc., and are commercially valuable materials. They, however, have a drawback of being intrinsically brittle, which is a common problem to phenolic resins. Thus, for example, in case where they are employed as molding materials, it has been difficult to produce molded products having complicated shapes or molded products of large sizes, since cracks are liable to occur in the resulting molded products.
Further, phenolic resins have been employed for molded products containing inserts, such as gripping parts of metallic tablewares, knives, forks, etc. In this case, conventional phenolic resins have been inferior in the metal insert properties, and particularly when molded products are produced at low temperatures as in winter season, cracks have been liable to occur on the contact surface of metals with phenolic resins, resulting in low production yield.
Still further, when phenolic resins are employed for laminated sheets, they are inferior in cold punchability. Thus, punching of such laminated sheets has been carried out by elevating their temperature up to about 120.degree. C. to soften them. In this case, however, when the temperature of the sheets is returned to ordinary temperatures after completion of the above hot punching, expansion shrinkage occurs in the base; hence the resulting products have dimensional errors and also warp etc. Thus it has been impossible to apply such sheets to the fields of electrical equipments requiring high performances.
Furthermore, even when phenolic resins are employed as various binders, for example, when they are employed as brake lining, etc., crack, break, etc. occur in the resulting brake materials, etc. Thus, it has been impossible to display full performances.
In addition to these various practical problems, the resins are very weak in the thermal impact at cold-hot repetitions. Thus, molding materials and laminating materials consisting of phenol resins have had a drawback that cracks readily occur through thermal impact at cold-hot repetitions.
Next, phenolic polymers will be mentioned. As for methods of employing the phenolic polymers, there are illustrated a method of adding a formaldehyde-generating compound such as hexamethylenetetramine thereto and subjecting the resulting mixture to heat treatment to obtain a cured product for use, and a method of mixing a phenolic polymer with an epoxy resin and further adding a curing accelerator for epoxy resins to the resulting mixture, followed by subjecting them to heat treatment to obtain a cured product for use. These cured products have a superior heat resistance, and some of them have now been commercially employed. These materials, however, also have a drawback of brittleness. Thus, when they are applied to molding materials, laminating materials, paints and lacquers, adhesives, various binders such as shell molds, grindstones, brake linings, etc., casting materials for e.g. ornamental goods, tools, tablewares, etc., foaming materials, etc., they have had drawbacks common to those of phenolic resins.
Heretofore, various studies have been made for overcoming the above-mentioned various drawbacks of phenolic resins, and various methods have been proposed. Among them, methods of modifying phenolic resins with rubbers have been widely carried out. For example there is a method wherein e.g. a novolak type phenolic resin is blended e.g. by roll kneading with a nitrile rubber consisting of units of acrylonitrile and butadiene, as a rubber having a relatively good compatibility, to prepare a resin having a nitrile rubber dispersed in a novolak type phenolic resin, and this resin is employed. Further, U.S. Pat. No. 3,536,783 discloses a rubber-modified novolak type phenolic resin prepared by uniformly dispersing a novolak type phenolic resin in a latex of nitrile rubber consisting of units of acrylonitrile and butadiene.
It is observed that the above-mentioned two problems, i.e. prevention of the resins from crack occurrence when the resins are employed as molding materials and punchability of laminated sheets prepared employing the resins have been improved by the above-mentioned methods of the prior art, but other various problems have not yet been solved as mentioned below.
Particularly, when molding materials, laminating materials, brake materials, etc. prepared employing the above-mentioned rubber-modified phenolic resins are employed under a condition of cold temperature, particularly -30.degree. C. or lower, the effectiveness due to the rubber-modification is lost and cracks are very liable to occur.
As for the crack occurrence caused by thermal impact through cold-hot repetitions, product having a sufficiently high impact resistance has not yet been obtained. For example, the problem is raised when they are employed in districts where temperature difference is large between day and night, or when they are employed at places subjected to repeated thermal impacts.
Further, the molding materials prepared employing the above-mentioned nitrile rubber are insufficient in the oil resistance and solvent resistance. For example when the molding materials are employed at places where they are always brought into contact with machine oils, solvents, etc., they are accompanied with fading of the surface of the molding materials and increase in the weight, and also reduction in the performances is notable.
Still further, in the finishing step of the molding materials where degreasing with trichloroethylene or the like is often carried out, trichloroethylene resistance is inferior, the surface condition is also inferior, particularly fading occurs, resulting in reduction of the quality of the molded products thus obtained.
Furthermore, for improving the metal insert properties of phenolic resins, an attempt of employing nitrile rubbers together with phenolic resins has been made. However, although the metal insert properties have been considerably improved according to the method, a practical problem has been raised because of its inferior solvent resistance. Namely, metal-inserted, molded products usually have oils, fats and fatty oils attached thereto, and for removing them, degreasing step of immersing them in a solvent such as trichloroethylene is indispensable. However, in the case of the molded products obtained according to the above-mentioned method, fading or color unevenness occurs after immersion in trichloroethylene. Thus, values as commodities have been notably reduced. When molding materials, laminating materials of phenolic resins obtained employing the above-mentioned nitrile rubbers are applied to certain uses such as electric parts to be subjected to a long time thermal hysteresis, a great deal of reduction in the physical properties occurs. Thus they have been restricted in their uses.